Position Determination of Mobile Stations in a Wireless Network

ABSTRACT

A network, and a method of operating a network. The network includes a plurality of stations each able to transmit and receive data so that the network can transmit data between stations via at least one selected intermediate station. Each station transmits probe signals in broadcast fashion to other stations to gather a list of neighbour stations. The stations transmit position data and/or position determining data in at least some of the probe signals. Each station maintains position data and/or position determining data received from selected probing stations, and utilizes the data to determine the absolute or relative position of itself and/or other stations. The stations can determine the relative or absolute position of other stations in direct communication with themselves, and also of other stations not in direct communication with themselves.

BACKGROUND OF THE INVENTION

This invention relates to a method of locating and determining theposition of wireless mobile stations in a communication network. For thepurposes of this specification, such a communication network will bereferred to as an Opportunity Driven Multiple Access (ODMA) network.

The determination of location is useful to service providers in theprovision of location based services to subscribers to a communicationnetwork. Such services include, for example, the provision of drivingdirection instructions, vehicle tracking, relevant regional informationand available applications; while also enabling categorization ofsubscribers for various purposes and for billing differentiation.

In addition, various regulatory authorities around the world now requirethat service providers of wireless telephone networks must be capable oflocating the users of the wireless telephones in order to facilitateemergency call processing.

These regulations mandate that the position of such users must beestablished to within predefined distances of their actual physicallocation. In the United States of America, for example, the FederalCommunications Commission promulgated wireless Enhanced 911 (E911) rulesrequire that service providers must be able to locate at leasttwo-thirds of the users of wireless telephones on their networks within125 meters of the users' actual physical locations.

The location of a wireless station in a network is generally determinedusing either network based location systems or station based locationsystems. Network based location systems typically utilize techniquesthat involve the triangulation of signals between the wireless stationsand fixed position base stations or access points, which act ascommunication ports between the wireless stations and the network.Station based systems may incorporate other technologies such as GlobalPositioning System (GPS) receivers that may be built into the wirelessdevices of the stations or used in combination with the devices.

It is likely that the need for service differentiation will grow inrelevance and that emergency regulation will possibly be extended towireless devices other than telephones. Consequently, accurate locationand positioning of the user stations has now become an essential featurein wireless networking environments. At present it is difficult tolocate certain of these devices, such as in the VOIP (Voice OverInternet Protocol) environment, without using positioning equipmenttogether with the wireless unit as there is no fixed relationshipbetween the VOIP device and the geographic position. In addition,positioning technologies are subject to limitations that may render thestations undetectable.

It is an object of the invention to provide accurate, continuouslocation and positioning information relating to wireless mobilestations, including VOIP and other traditionally undetectable devices,using a network based methodology that is not dependent on base stationsand access points.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of operating anetwork comprising a plurality of stations each able to transmit andreceive data so that the network can transmit data between stations viaat least one selected intermediate station, the method comprising:

-   -   transmitting probe signals from each station;    -   transmitting position data and/or position determining data in        at least some of the probe signals, the position data including        data indicative of the absolute or relative position of a        station transmitting a probe signal, and the position        determining data including data usable by a station receiving a        probe signal to determine the absolute or relative position of        the station and/or other stations;    -   maintaining, at stations which receive probe signals from one or        more probing stations, position data and/or position determining        data received from selected ones of the probing stations; and    -   at each station maintaining said position data and/or position        determining data, utilizing the position data and/or position        determining data to determine the absolute or relative position        of said each station and/or other stations.

The position data and/or position determining data in the probe signalsmay include data indicating the absolute position or relative positionof nearby stations selected by the station transmitting the probesignals.

The position data and/or position determining data may be used todetermine the relative or absolute position of other stations in directcommunication with said each station, and also other stations not indirect communication with said each station.

The method may be operated in a communication network in which thestations can transmit a message from an originating station to adestination station via at least one opportunistically selectedintermediate station.

Alternatively, the method may be operated in a network providedprimarily for purposes of tracking or locating stations in the network.

The method may include selecting, at each station, a channel for thetransmission of probe signals to other stations, other stations whichreceive the probe signals from a probing station responding directly, orindirectly via other stations, on the selected channel.

The method may include transmitting clock data in the probe signals, andutilizing the clock data to determine the time taken for the probesignals to propagate between stations and hence the distance betweensaid stations.

The method may further include synchronizing clocks at the stations ofthe network, with updated timing data for this purpose being transmittedfrom a central timing authority to the other stations.

The acceptance or rejection of said updated timing data at any stationmay be determined in response to a cumulative error function calculatedin respect of the transmission of such data, relative to other prior orsimultaneous transmissions of such data received at said station,thereby maintaining a high level of accuracy in respect of thesynchronization of clocks at each station of the network.

The position data may comprise position information indicating theposition of one or more stations to a predetermined degree of accuracy.

The position data may comprise absolute position information obtainedfrom a station equipped with a station based positioning system, or astation with a known fixed location.

Alternatively or in addition the position data may comprise relativeposition information indicating the position of one or more stationsrelative to other stations.

The relative position information may be obtained by stationsdetermining the approximate distance between themselves utilizingtransmission power and/or path loss data in probe signals transmittedbetween such stations.

Alternatively or in addition the relative position information may beobtained by stations determining the distance between themselvesutilizing timing data extracted from probe signals transmitted betweenthe stations.

The timing data may include processing delay data inserted into replyprobe signals by stations responding to received probe signals, theprocessing delay data indicating the time taken at a station respondingto a received probe signal to process the received probe signal.

The method may include obtaining position information indicating theposition of one or more stations by triangulation.

The method may comprise utilizing a combination of absolute and relativeposition information to determine the absolute position of furtherstations by determining their position relative to other stations thathave previously determined their own absolute positions, so that suchfurther stations that are unable to communicate directly with otherstations that have absolute position information can neverthelessdetermine their own absolute position indirectly.

The method may include providing a number of seed stations, each ofwhich is able to determine, or is provided with absolute position datadefining, its own absolute position with relatively high accuracy, otherstations transmitting probe signals to and receiving probe signals fromthe seed stations thus obtaining absolute position information from theseed stations to determine their own absolute positions, and furtherstations transmitting probe signals to and receiving probe signals fromsaid other stations thus obtaining absolute position information fromsaid other stations to determine their own absolute positions.

Each station may select received probe signals from which to extractposition or timing data according to the extent to which such receivedprobe signals are determined to contain position or timing data of ahigh quality in terms of distance measurement capability or clocksynchronization.

The method may comprise analyzing received probe signals to determinewhether or not they are transmitted during optimum peaks of opportunity.

The method may comprise measuring path loss and/or multi-path distortionin such received probe signals, and selecting probe signals having lowpath loss and/or low multi-path distortion for extraction of position ortiming data therefrom.

Stations may include data in their probe signals relating to the lengthof time they have remained static, other stations receiving the probesignals utilizing position data and/or position determining datapreferentially from stations that have remained static for the longestperiods.

Stations may include auxiliary data in their probe signals relating toone or more of the following: the number and/or quality of transmissionhops between stations identified in the probe signals; age dataindicating the age of timing data or position data and/or positiondetermining data included in the probe signals; the stated or determinedlevel of accuracy of position information relating to one or morestations identified in the probe signals; and quality data indicatingwhether the probe signals have been sent at peaks of opportunity, otherstations receiving the probe signals utilizing position data and/orposition determining data therein selectively depending on the nature ofthe auxiliary data included in the received probe signals.

The probe signals may be transmitted on probe channels defined by acentral authority, thereby reducing interference and preventing jammingor interception of the signals.

Stations may maintain historical position data of other stations for apredetermined time after such other stations have lost connectivity withone another, the historical position data being retrievable to determinethe last known position of a station with which connectivity has beenlost.

Stations may utilise variations in data in probe signals or othercharacteristics of the probe signals, arising out of relative movementbetween stations, to resolve ambiguities in relative position dataand/or position determining data in the probe signals.

The nature or quality of a service available from a station in thenetwork may be adjusted according to the determined absolute or relativeposition of said station and/or other nearby stations.

For example, the method may include providing information to a user of astation relating to facilities, objects or persons, or other stationsnear to the determined position of said station.

In one embodiment of the method a first station requiring positioninformation relating to a second station that is moving relative to thefirst station may transmit gradient gathering probe signals addressed tothe second station, directly or via one or more intermediate stations,at an increased rate selected to provide enhanced resolution of theposition information.

The gradient gathering probe signals may be transmitted at an increasedrate only while the first station requires the position information.

The increased rate of transmission of the gradient gathering probesignals is preferably at least an order of magnitude greater than astandard rate of transmission thereof.

A first station requiring position information relating to anotherstation in the network may transmit a position request message addressedto a central authority maintaining position data and/or positiondetermining data of stations in the network; to one or more neighbors ofthe first, requesting station for onward transmission to the otherstation; or directly to the other station.

The station whose position is required may transmit a reply message tothe first station via the network with the required positioninformation.

The first station may transmit a gradient gathering probe signaladdressed to the other station via one or more intermediate stations,said other station transmitting a response via one or more intermediatestations to thereby create a gradient through the intermediate stations,the gradient providing information enabling a relative or absolutedirection vector to be established between the first station and saidother station.

Further according to the invention there is provided a networkcomprising a plurality of stations each able to transmit and receivedata so that the network can transmit data between stations via at leastone selected intermediate station, wherein each station in the networkcomprises a transmitter, a receiver and data processing means and isoperable to:

-   -   transmit probe signals to other stations and receive probe        signals from other stations;    -   transmit position data and/or position determining data in at        least some of the probe signals, the position data including        data indicative of the absolute or relative position of a        station transmitting a probe signal, and the position        determining data including data usable by a station receiving a        probe signal to determine the absolute or relative position of        the station and/or other stations;    -   maintain, at stations which receive probe signals from one or        more probing stations, position data and/or position determining        data received from selected ones of the probing stations; and    -   utilize the maintained position data and/or position determining        data to determine the absolute or relative position of said        station and/or other stations.    -   including other stations in direct communication with said        station, and also other stations not in direct communication        with said station.

Each station may be operable to determine the absolute or relativeposition of other stations in direct communication with said station,and also other stations not in direct communication with said station.

Each station preferably includes a clock and is arranged to transmitclock data in the probe signals, and to utilize the clock data todetermine the time taken for the probe signals to propagate betweenstations and hence the distance between said stations.

The network may include a central timing authority for transmittingupdated timing data to the stations of the network, and wherein eachstation is arranged to synchronize its clock with the clocks of otherstations of the network utilizing the updated timing data.

Each station is preferably arranged to accept or reject said updatedtiming data according to a cumulative error function calculated inrespect of the transmission of such data, relative to other prior orsimultaneous transmissions of such data received at said station,thereby maintaining a high level of accuracy in respect of thesynchronization of clocks at each station of the network.

At least some stations in the network may comprise a station basedpositioning system or be programmed with position data corresponding toa known fixed location.

Each station may be adapted to determine the approximate distancebetween itself and other stations utilizing transmission power and/orpath loss data in probe signals transmitted between the stations.

Alternatively or in addition each station may be adapted to obtainposition information indicating the position of one or more otherstations by triangulation.

The network may include a number of seed stations each able to determineits own absolute position with relatively high accuracy, so that otherstations transmitting probe signals to and receiving probe signals fromthe seed stations can obtain absolute position information from the seedstations to determine their own absolute positions, and further stationstransmitting probe signals to and receiving probe signals from saidother stations can obtain absolute position information from said otherstations to determine their own absolute positions.

The data processing means of each station is preferably operable toanalyze received probe signals to determine whether or not they aretransmitted during optimum peaks of opportunity.

The data processing means is preferably operable to analyze receivedprobe signals by measuring path loss and/or multi-path distortion inreceived probe signals, and to select probe signals having low path lossand/or low multi-path distortion for extraction of position or timingdata therefrom.

The network may include a central authority to define probe channels forthe transmission of the probe signals, to reduce interference andprevent jamming or interception of the signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in detail in the followingpassages of the specification, which refer to the accompanying drawings.The drawings, however, are merely illustrative of how the inventionmight be put into effect, so that the specific form and arrangement ofthe features shown is not to be understood as limiting on the invention.

FIGS. 1( a) to (d) are schematic diagrams showing known methods ofdetermining distance and position of a station from one or more stationshaving position information;

FIGS. 2( a) and (b) are simplified schematic diagrams showing a numberof stations operating in an ODMA network; FIG. 2( a) showing the generalposition of the stations at a time t₀ and FIG. 2( b) showing the samestations having subsequently gathered up to three close neighbors;

FIGS. 3( a) to (e) are simplified schematic diagrams showing the samestations as in FIG. 2, the sequence represented in FIGS. 3( a) to (c)illustrating the stations gradually determining their positions at timest₀, t₁ and t₂ respectively according to a first embodiment of theinvention; and in FIGS. 3( d) to (e) according to a second embodiment;

FIGS. 4( a) to (e) are schematic diagrams illustrating distance andposition determining techniques utilized in accordance with the firstembodiment of the invention;

FIGS. 5( a) to (e) are schematic diagrams showing developments of theconcepts illustrated FIG. 4, in a three dimensional orientation;

FIGS. 6( a) to (f) are a sequence of simplified connectivity diagramsshowing the mechanism used by stations in an ODMA network whentriangulating position in accordance with the second embodiment of theinvention;

FIG. 7 is a simplified schematic diagram showing a subset of thestations of FIG. 2, showing certain of the stations having gatheredneighbors through probing;

FIGS. 8( a) and (b) are simplified schematic diagrams showing theposition determining mechanisms of stations having sufficient fixedabsolute position neighbor stations from which to triangulate their ownabsolute positions in accordance with the second embodiment of theinvention;

FIGS. 9( a) to (d) are simplified schematic diagrams showing theposition determining mechanisms used by stations of FIG. 7 not havingsufficient neighbor stations from which to triangulate position;

FIG. 10 is a simplified schematic diagram showing an alternativetechnique employed by the stations of FIG. 9, in accordance with thesecond embodiment of the invention;

FIG. 11 is a simplified schematic diagram showing an alternativetechnique employed by the stations of FIGS. 8 to 11; and

FIGS. 12( a) and (b) are simplified schematic diagrams similar to thoseof FIG. 5, showing methods of obtaining a distance gradient or positiongradient.

DESCRIPTION OF EMBODIMENTS

As stated above, systems for locating wireless mobile stations in awireless network are generally network based or station based. Networkbased systems use the information gathered to perform triangulation ortrilateration (or similar) calculations to establish the position ofstations having unknown locations, typically relative to known fixedabsolute positions. Station based systems incorporate other technologiesbuilt in to the mobile wireless stations, or that are used inassociation with the mobile stations, to locate position. Suchtechnologies include Global Positioning System (GPS) receivers, whichmay be enhanced with the provision of additional ground based stations.However, in practice GPS and the other technologies have certainlimitations, the most significant of which is the fact that it may beunavailable in certain topographies, in buildings or underground forexample.

Unless otherwise indicated by the context, the term “absolute position”in this specification is intended to refer to a position that isgeographically referenced (irrespective of the accuracy thereof, such asa position being indicated with reference to a defined grid orcoordinates. For example, absolute position could be defined in terms ofa reference position in the x, y and z planes, or in terms of latitudeand longitude (and possibly elevation) coordinates. The term “relativeposition” is intended to refer to a position expressed in terms of therelative distances between, and relative orientation of, stations in thenetwork, with reference to one station or to each other, but withoutreference to a defined grid or coordinates.

The present invention relates to a network based method of locating andpositioning mobile stations, typically for use in an ODMA communicationnetwork (of the general kind described in WO 96/19887 entitled Multi-HopPacket Radio Networks). Some of the stations in the network may havestation based positioning systems, but this is not a requirement of theinvention.

In order to perform triangulation and related geometric calculations,stations must be able to determine the distances between the stations.There are a number of known mechanisms for determining the distancebetween two wireless stations in a network environment. These mechanismsinclude:

-   -   signal timing analysis, by measuring the time of arrival (TOA)        of signals between the stations which, together with position        detecting equipment, enables calculation of the time difference        of arrival (TDOA) of signals and estimated position;    -   angle of arrival analysis (AOA), which measures the angle of the        signal between stations; and    -   radio propagation analysis, which evaluates radio frequency        characteristics such as frequency shifts, phase shifts and path        loss of the weakening signal between stations on the network.

In a radio network, path loss information provides an initial indicationof the distance between the two stations through basic and well knownradio propagation analytical techniques relating path loss to distance.Thus, if a station hears a probe signal transmission of a neighborstation, the receiving station will determine that the transmittingneighbor is a certain distance away by analyzing the power level of theinitial transmission and the noise floor specified in the probe,although the mechanism has limits in accuracy. The degree of accuracy isa function of the distance; being less accurate with increasingdistance.

Each station listening to the probing transmissions of other stationsand to any responses will have initial information in respect of thedistance of other stations from the listening station and to each other(information in the probes and responses). However, if the probeinformation that is received incorporates information about thelistening station itself, in other words, it provides information thatit obtained from listening to probes from neighboring stations, then thelistening station can make more accurate conclusions about the distancebetween the stations. If responses are then received, in reply toprobing, the responses will provide specific information that willenable very accurate determination of distance through radio propagationanalysis techniques or from timing measurements.

Consequently, although the receiving station will not know exactly whereit is relative to the neighbor, it will at least recognize that it iswithin a certain radius of a circle (more accurately a three dimensionalsphere) generated by the probing station at a known radius away.

While this may not at first seem especially accurate, if the otherstation is in fact a very short distance away, this information may wellbe accurate enough. In an ODMA network environment this will often bethe case. For example, two mobile telephone users may be in a crowdedroom, in which case although the exact position is not available, oneuser will be able to establish that the other user is at least within acertain distance of the user's own position. In other words, althougheach user may not know the exact actual position of the other, they willknow that they are in the same room and no more than a few meters away.

This concept is shown in FIG. 1( a), where a transmitting station X is adistance x away from a receiving station R. If station X has a knownfixed absolute position that it can communicate, the receiving station Rwill know that it is within the radius x (and therefore in one of thenine grid blocks marked A-C/3-5). If the station X does not have adetermined position, R will at least know that it is a relative distancex from X but will not have any position information.

If there are two neighbors of R with known fixed absolute positions,analysis by the receiving station will lead to the conclusion that thereceiving station is at one of two possible intersections of the circlesdefined by the radii from the two stations. This is illustrated in FIG.1( b), where a second station Y is a distance y away from the receivingstation R; leading to the conclusion that the receiving station is ineither location B/3 or C/5. Again, if the grid blocks are very small,this may already provide sufficient information for positioningpurposes.

If the other two stations (X and Y) did not have absolute positioninformation, and assuming X and Y were not within range to receivetransmissions from each other, then R would only know that it was withina distance x and y from X and Y respectively. However, if X and Y werethemselves able to pick up transmissions from each other they would beable to establish their relative positions in relation to each other asa vector (distance and direction) irrespective of the ambiguity in theposition of R. This concept is expanded upon below in this specificationwith reference to the present invention.

Known information regarding the region may enable certain assumptions tobe made about the likelihood of the station being at one or other of thetwo possible locations (for example the one location may be a road andthe other a swamp). However, it will be understood from the descriptionthat follows in this specification that the ODMA slow probing andneighbor gathering processes will also assist in resolving these formsof ambiguity without requiring any actual knowledge of the region ortopography.

FIG. 1( c) shows that if a third station Z with fixed absolute positionis a calculated distance z away, then the location of the receivingstation R can be narrowed down to a fixed absolute point in locationC/5, through basic triangulation calculations. Again, if no absoluteposition information is available at the stations X, Y and Z, then all Rwill be able to determine is that the stations are within a distance x,y and z from R, respectively. (The positions of the stations X, Y and Zrelative to each other could be determined if they could hear eachothers' transmissions.)

Obviously, the triangulation calculations used in the example of FIG. 1can also be applied to determine the third dimension of the relativeelevation of the stations when an additional station is involved. Theuse of directional antennas will reduce the number of transmittingstations required for positioning purposes by using angle of arrivalanalysis. These methods involve known techniques.

FIG. 1( d) shows the wireless station R requiring position informationand stations X, Y and Z at respective new positions X′, Y′ and Z′. Atthis point the wireless station R is using a new neighbor W from whichto determine its position, together with stations X and Y. Station Zcould either be out of range (as illustrated) or could be used toprovide additional information that would enable the wireless station Rto test its position calculations.

It can be seen that in the above explanation a station in an ODMAnetwork can establish its location by obtaining information from thestations that it has established as its neighbors. Alternative methodsof determining distance (such as timing probes and responses, asdiscussed below) may be utilized that provide greater accuracy, but theprinciples described above will still apply.

In traditional network based position determining mechanisms, a stationattempting to establish its position will try to communicate with fixedposition beacons that are in range of the station and which haveabsolute position information. In some more advanced systems, if thestation fails to locate enough beacons to determine its position, it mayattempt to locate other stations in the region that are themselves incontact with beacons in order to estimate position.

However, this utilization of the beacons as touchstones is not requiredin the present invention, where the stations do not start by attemptingto communicate with beacons, but instead simply start gathering goodquality neighbors regardless of the absolute position information thatmay be around them. Some of these neighbors may well turn out to bestations with absolute position information, but this is not required assuch.

When switched on, all a station needs to do is listen for probe signalsand probe for neighbors in order to gather and maintain a predefinedgroup of the best neighbor stations available. The positioning mechanismis not dependent on coverage from any base station, fixed position orother datum point. If the neighbor happens to have absolute positioninformation, then the station will itself be able to determine itsposition very quickly.

For reasons that will become apparent, where a station is activated in apre-existing network the stations already operating around the newstation are very likely to have already established their positions(whether relative or absolute). However, in the illustrated embodimentsit will be assumed that many (if not all) of the stations will need toestablish position. As stations are not all attempting to communicatewith a limited number of stations with position information (as is thecase with beacons), the present invention has the additional benefit ofnot overloading the network with these unnecessary transmissions.

The ODMA-over-wireless methodology is used in a communication networkwhich has a number of wireless stations which are able to transmit datato and receive data from one another. The methodology comprises defininga first probing channel for the transmission of first, broadcast probesignals to other stations. Other stations which receive the first probesignals (also referred to as “slow probes”) from a probing stationindicate to the probing station their availability as destination orintermediate stations. A neighbor table comprising details of, andconnectivity data relating to, these other available stations ismaintained at each of the stations.

In an ODMA network utilizing a wireless medium, when there are a numberof stations in close proximity they will end up probing at higher datarates and lower transmit powers. Listening stations will occasionallyrespond to stations that are probing at the lower data rates, or that donot have enough neighbors, to help any lonely (distant) stations (alsoreferred to as “lonely neighbors”) that cannot use the higher data ratesor do not have sufficient neighbors. Stations will only use the lowerdata rates when they are lonely and cannot find sufficient neighbors atthe higher data rates and at maximum power.

ODMA networks utilise two kinds of probing processes, “slow probing” and“fast probing”. The slow probing process is used by each network stationto gather neighbors, while the fast probing process is used to constructgradients between originating and destination stations.

Each station will transmit slow “neighbour gathering” probe signals atregular intervals (determined by a Slow Probe Timer) trying to findother stations. Stations indicate in their slow probes that they areable to detect other stations probing and in that way stations will varytheir probe power until a certain predetermined number of stationsindicate they are able to detect the probes. If a station never acquiresthe required number of neighbors it will remain at the lowest data rateand maximum transmit power.

Each station will randomly vary the Slow Probe Timer slightly betweenslow probe signal transmissions to avoid collision with other stations.Should any station start receiving another station's transmission, itwill reload the Slow Probe Timer with a new interval.

In a wireless network of mobile stations the stations are constantlymoving, and as such the number of neighbors will constantly be changing.If the number of neighbors exceeds the required number, a station willstart to increase its data rate on the probing channel. It will continueto increase its data rate until it no longer exceeds the required numberof neighbors. If it reaches the maximum data rate it will start to dropits slow probe transmit power by small increments until it eitherreaches the minimum transmit power, or no longer exceeds the requirednumber of neighbors.

When a station replies to another station's slow probe on a ProbingChannel it will limit the length of its data packet to the Slow ProbeTimer interval. This is to avoid other stations probing over its reply.If the station that is replying has more data to send than will fit in asmall packet it will indicate in the header of the packet that the otherstation must move to a specific Data Channel.

There can be a number of Data Channels defined for each Probing Channel.The station that is requesting the change will randomly select one ofthe available Data Channels. When the other station receives the requestit will immediately change to that Data Channel, where the two stationswill continue to communicate until neither of them have any data tosend, or if the maximum time for remaining on the Data Channel expires(set by a Data Timer). Alternative data transport protocols could alsobe used.

When a station changes to the Data Channel it loads the Data Timer. Itwill remain on the Data Channel for as long as the Data Timer willallow. When the Data Timer expires the stations will revert back to theProbing Channel and start probing again.

The slow probing process consists of three basic functions:

1. Neighbor collection2. Power learning3. Ramping of neighbors

The process of neighbor collection consists of a station probing atincreased levels of power until neighboring stations indicate in theirown probes that they are detecting the probes of the first station. Thepower of the probe is increased until a predetermined number ofneighbors indicate that they are detecting the probes.

All probing stations increase and decrease their probe power until allstations have collected a predetermined number of neighbors. Thisprocess consists of increasing and decreasing the power level of probesand indicating in probes which other stations' probes are heard. In thisway all stations can learn what power level they require to reachvarious neighbors.

Each time a station probes it indicates its transmit power and noisefloor and which stations it has as neighbors. Every time a station hearsanother station probe it calculates from the probe the path loss andpower required to reach the station from the path loss and the noisefloor of that station. The path loss to the neighbor and the powerrequired to reach the neighbor are stored in the neighbor table kept ateach station. If a neighbor is no longer heard then the path loss andpower level required to reach the station are increased or “ramped” inthe table until a certain level is reached at which point the neighboris removed from the neighbor table.

If a station has a message (or other data) to transmit to a station thatis not one of its neighbors, for example, a distant station across thenetwork, it begins to transmit fast probe signals (or gradient gatheringprobe signals) to develop information on how to reach that station. Theinformation is called a gradient and is an indication of the cumulativecost to reach a destination station. When a station starts to fast probeit indicates that it is looking for a destination and neighbors hearingthe fast probe will themselves fast probe until the destination stationhears the fast probes of its neighbors. The gradient is then builtthrough adding cumulative cost until the gradient reaches the source,and the source can commence to send messages to neighbors using theinformation developed in the gradients to destination, which in turn cansend them to their neighbors until the destination is reached.

Each station keeps a record of the (cumulative cost) gradients to eachdestination of each of its neighbors, and its own gradient to thedestination. In standard ODMA communications, each station only passesmessages to stations with a lower cumulative cost to destination. Astation can pass a message to any of its neighbors with a lower gradientto destination. Neighbor gathering via slow probing and gradientgeneration via fast probing allow a station to develop a number ofchoices of stations with lower cost to any destination that can sendmessages to such destinations. The neighbors are maintained all the timevia slow probing and gradients are only developed on a needs basis whenmessages/data needs to be sent to stations that are not neighbors.

The ODMA methodology, particularly with regard to the use of neighbortables and gradient tables, is described in detail in WO 2005/062528entitled Probing Method for a Multi-Station Network, In the presentinvention the fast probe process described in that document could beused in a similar manner to define a position gradient or distancegradient through levels of neighbors with highest level of confidence inrespect of position determining accuracy to the destination, based ondefined position-relevant cumulative error functions.

The probing process provides a considerable amount of information aboutthe neighbors of each station—and indeed about the neighboring stationsof each of the neighbors. In the present invention, the identificationand maintenance of good quality neighbors is a key element indetermining the accuracy of the positions calculated and consequentlythe ODMA neighbor gathering process through slow probing is the primarymechanism used to assist in the locating and positioning of a wirelessstation in the ODMA network. Each wireless station uses the slow probingprocess to identify and obtain information from the station's neighbors.A station is considered a “neighbor” in this sense if it has been heardto transmit a neighbor gathering probe message, and details of theneighboring stations identified will be maintained in each station'sneighbor table.

If an identified neighbor has itself transmitted a neighbor gatheringprobe message that is received by a particular station, and the probecontains information of the particular station's own identifier, thenthe neighbor is flagged as a “detecting neighbor” in the neighbor table.Typically each station will adapt its neighbor gathering techniques(generally by increasing data transmission rates and by powering downthe strength of the probe signals sent out) to maintain approximately 10detecting neighbors. Of these, a predetermined number of the neighborswith the lowest path loss are flagged as “close neighbors” (for example,five stations). The information obtained from close neighbors may betreated differently or preferentially and the techniques used totransmit the information may also be adapted depending on the neighbors.

If a station is unable to acquire the minimum number of close neighborswhen it is transmitting on full probe power, it is referred to as a“lonely neighbor”. Other stations that have acquired the required numberof close neighbors that can detect the lonely neighbor transmissionswill let the lonely neighbor know that they are detected, and mayprovide additional information to the lonely neighbor.

When not probing or sending other messages, each station is listeningfor the probes of the other stations. When heard, the receiving stationcan use the transmit power information provided in the probe toestablish the path loss to the station. As each station is constantlyidentifying the close neighbors with the lowest path loss, theseneighbors are likely to be either in direct line of sight, or have thebest signal with least interference.

Even stations merely able to listen will be in relatively goodconnectivity with a probing station in a fully operational network withmany stations, as stations sending probes will likely have powered downtheir transmission levels in order to minimize their number ofneighbors. In other words, neighbors are typically chosen for thequality of connectivity. Lonely neighbors are the exception, but will berecognized by the stations (hearing their full power transmissions anddetermining that they have less than the required number of collectedneighbors) and assisted.

Furthermore, the broadcast probes can include information of thebroadcasting station's close and/or detecting neighbors. This enablesthe stations listening to the broadcasts to know the positions of theneighbors and this facilitates scavenging of additional information.Indeed, the listening station could even probe specific stations fromthe information derived in this manner if required.

By analyzing the information available at a station it should be clearthat some simple assumptions can be made from path loss and signalstrength information. If there is a very low path loss, it is likelythat the stations are in direct line of sight (without any reflectedsignals). In such an instance, the distance between the stations can bedetermined with relatively high accuracy. This will provide a “raw”determination of distance and position. The slow probing methodologygathers this information in the ordinary course of operation of an ODMAnetwork, together with information regarding any delays. The strongestsignal is generally the direct signal although there may be unusualcircumstances where this is not the case. It will be seen below thatthis form of potential ambiguity will be recognized and resolved due tothe mobility of the stations.

If path loss is high, assumptions can be made about the environment—forexample there could be interference, barriers (such as buildings) or thestations might simply be far apart. If a delay is registered,assumptions can be made that there is a reflected or deflected signal.As there are likely to be several neighbors in an ODMA network, itshould be possible to establish position from several independentsources and verify information from other stations, and thus errorscaused by distance calculations based on reflected or deflected signalscan be obviated.

Depending on the distance, different power and modulation techniques maybe utilized. If stations are close by, sharp broadband pulses can betransmitted from which distance and position can be very accuratelyestablished. While wide spectrum or broadband signals allow higher datatransmission rates, the signals become blurred over increasing distanceunless the power is increased. Modulation techniques may improve theseproblems to some extent, but to travel greater distances a narrowedbandwidth at lower data rates and increased power is required. Theprobing methods used in the ODMA communications already adapt thesecharacteristics to optimize transfer of data, and can also be used toenhance positioning calculations.

In addition to their use in estimating the distance between stationsfrom the path loss and signal strength characteristics, specific probesmay be sent to neighbors to obtain timing information relating to thetime taken for the probe signal to travel from the one station to theother and back again. Provided that each station has a very accurateclock incorporated in the unit, the times taken for the probe to be sentto another station (the delta time), then to be processed at thereceiving station and then to be returned, can be used to calculatedistance using the speed of light (also being the speed of propagationof radio signals).

In the ODMA environment, a probe signal may be sent out to any neighboridentified in the neighbor gathering process, with the probeincorporating a timer. This probe may be separate and distinct from theneighbor gathering probes, or the neighbor gathering probes may containthe timer so that the neighbors listed as close neighbors will respond.On receipt, the neighbor records the time the probe is received and thetime when the reply is returned after processing. Whether the probedstation returns the actual times of receipt and sending of the response,or that station simply returns just the processing time as such, itshould be evident that by excluding the processing time at the probedneighbor station, the probing station can calculate the time taken for aradio signal to reach the neighbor and return (in other words, twice thedistance between the stations). The speed of light is approximately3.0×10⁸ m/s, so if the calculated time for a signal to reach theneighbor is 1 μs the distance between the stations is 300 m.

Consequently, for location and positioning purposes, in addition to thecharacteristics of general purpose neighbor gathering probes requiredfor ODMA communication, clock or timing information can be placed in theprobe with the unique ODMA identifier/address of each known neighbor.Each station will hear broadcast probes from immediate (close anddetecting) neighbors and independent clock or timing data will be sentback to each of the probing neighbors. In this manner, both the sendingand receiving neighbors will have ongoing information regarding theirrelative distances from each other and will be able to maintain theaccuracy of their relative positions.

As accurate transmissions are required for time-based positioningtechniques, short transmissions with accurate time datum points arenecessary. Well defined sets of bits in the transmission start theclocks at the respective stations when the sets are picked up in theprobe and again when sent back to the probing station, with an injectedunique bit sequence in the transmission effectively acting as a trigger.This requires sophisticated hardware control, but enables the very fastresponses of the digital clocks available to start counters and measuretime very accurately.

When a probing station sends a transmission, the specific bit sequencetriggers the probing station's clock to start, and the probing stationthen waits for a response. The unique bit sequence is then picked up atthe probed station, which starts a clock at the probed station thatmeasures the turnaround processing/delay time after receipt of thetrigger at this station, until the probe response is sent back to theprobing station. When this occurs, the trigger bit sequence is againset, and the turnaround time is reported in the transmission. On receiptof the transmission at the probing station, the trigger bit sequencestops the clock at the probing station, which subtracts the turnaroundtime at the probed station as reported; and consequently the duration ofthe round trip (excluding the processing turnaround time) is known. Fromthis information the station can calculate the distance between thestations.

As illustrated above, the stations do not necessarily need to have auniversal clock to determine distances between them, but it would bepossible to update and synchronize all the stations from one especiallyaccurate clock on an ongoing basis if this is desirable. To achievethis, a time transmission could be sent out from a reference stationacting as a central time authority to provide each station with theexact time.

It must be appreciated that a transmission could have been received overa particular hop that had poor connectivity, in which case there will besome uncertainty regarding the setting of the clocks' time and thetiming that is calculated for distance determination. The lack of timingaccuracy or of synchronicity of the stations' clocks, or poortransmission quality, can all contribute to an inaccuracy factor. Thisinaccuracy factor is an error function that is a form of cost functionassociated with each hop. These error functions can be aggregated overmultiple hops as the transmission progresses, which provides anindicator regarding the certainty (cumulative error function) of thecalculations based on the information derived.

In order to reduce the effect of drift in the determination of the timetaken over multiple hops, the time delay (caused by each stationprocessing the communication) for each hop is determined. As stationswill not necessarily know how long it took for the message to arrive, aprobe could be sent to the reference station and, from the responsereceived, the station updating the time will be able to calculate thedelay. This information could be incorporated in the actual time set forsynchronization purposes at each station. A station could obviously alsorequest the correct time from the reference station and then time thedelay in receiving the response.

The time synchronization could be performed via many hops from thecentral time authority, and this synchronization could be revised atregular intervals or on an ongoing basis to minimize the effects ofclock drift. In order to achieve this, time updates could be radiatedout by the central authority and broadcast to the stations on thenetwork using the gradient updating techniques described in WO2005/062528 entitled Probing Method for a Multi-Station Network,referenced above.

As the central authority radiates out the clock updates, stationsreceiving the time or clock update data could choose to accept theupdate if the cumulative error or cost function is better than thatreceived in a previous update. In other words, if the level ofuncertainty regarding the integrity of the transmission is determined tobe worse than that of earlier updates, the information could bedisregarded in favor of the older information which is considered moreaccurate. The cumulative cost function description disclosed in WO2005/062528 is relevant in the application of this invention as well.Obviously, a transmission with time update information received over onevery long hop may well have a higher cost function than a transmissionover several hops of good quality. Consequently, where a transmissionmay be made over two potential routes, the path with the lowercumulative cost will be preferred as the distance determination will bemore accurate. Therefore the value of any distance calculations can beprioritized based on the aggregated cost over the hops, or in terms ofthe number of hops required, or both.

To counter the effects of the inaccuracy and the increasing error/costfunction, each station can ascertain whether the clock available at theproposed receiving station is more or less accurate than the clock atthe transmitting station. As all the neighbors are passing their clockdata between them, the possibility of looping must be avoided (in otherwords, when an update is received that was initiated by that samestation). WO 2005/062528 describes techniques for preventing thislooping through “freezing”. Essentially, to avoid the loop, a counterwill be initiated in the probes that will register the number of timesthe updated timing data has been passed between stations, therebyenabling each of the stations to recognize how up to date the timinginformation is, so that the use of less accurate timing information isavoided.

It will be appreciated that the maintenance of an accurate local clockat each station greatly simplifies distance calculations. The level ofaccuracy required in respect of the distance calculation will dictatethe level of accuracy required in respect of the clock. By way ofillustration, if a resolution of 30 m is required, the clock must beaccurate to 0.1 microseconds (100 nanoseconds).

The operation of the network as a whole is also simplified considerablyif all the stations have local clocks with synchronized times. Inaddition to the improved determination of distance, the synchronicity ofthe clocks provides other benefits. For example, communication ispotentially more effective if stations hop between frequencies todifferent channels, as this avoids interference. However, thecommunicating stations must move channels simultaneously, or in apredetermined sequence, for this to be effective. If all the stationsinvolved have synchronized clocks, then this form of communication ispossible over the network.

Moreover, synchronicity facilitates the provision of services andnetwork management in absolute time, enabling the central authority torequest that certain stations move to certain channels at certain timesin order to receive information, such as software or security updates,etc. Again, this would minimize interference in the network as a wholeand additionally improve privacy. Hopping channels could take place inresponse to a schedule (which could be determined randomly by thecentral authority and communicated in encrypted form to the stations)and this form of control is obviously an important consideration innetwork management and for service quality levels. However, to beeffective, all the stations involved must be capable of reactingaccurately when required to do so.

Regardless of whether the distance between stations is calculated fromsignal timing or propagation analysis (or any other analysis over theair interface), the other stations may provide position information tosome stated level of accuracy. Position information could be provided asx/y/z coordinates on a predefined reference framework, or simply aslatitude and longitude (to degrees, minutes and seconds), calculatedfrom position reference datum points (determined through GPS positioningsystems, for example, together with a means of establishing elevation ifdesired). Any suitable referencing, map, grid or co-ordinate system maybe utilized.

As the ODMA process makes use of “peaks of opportunity”, it is possibleto select probe signals that have low path loss, low multi-pathdistortion and “high quality” in terms of measurement distancecapability or in the time synchronization. (Peaks of opportunity arisewhere peaks in the signal strength or signal-to-noise levels areidentified by monitoring physical characteristics of received signals orby monitoring bit error rates as a function of time, so thattransmission power between stations can be reduced, which reducesinterference and reduces the necessity for the retransmission ofmessages. These peaks may be due to factors such as variations in signalpath amplitude, frequency or phase variation, noise or interference,multi-path effects, etc.) If these probe signals using peaks ofopportunity in terms of distance calculation are used, then the distancemeasured is considerably more accurate. Consequently, it should beappreciated that not every probe signal need be used, but rather thoseprobe signals sent at optimum peaks of opportunity should be used. Thiswould be especially applicable in very simple single hop situations.

It will be appreciated that the probing channels used by the stationscould be changed as well, upon request or in accordance with apredetermined schedule for this purpose. This would reduce interferenceand prevent any third party attempts to block or access the signals.Moving the channels over which the probe signals are transmitted makesit more difficult to jam or intercept the signals. Therefore the signalsare more secure and private. As stated above, the changing of probingchannels requires accurate timing.

Ultimately, the distance calculations required involve fundamentals ofsimple geometry. In the ODMA network, among the many subscriberstations, there is a relatively small proportion of wireless “seed”stations that are interspersed within the region being covered. Theseseed stations are not points of access or base stations that may beprovided in more typical wireless networks, like cellular telephonenetworks or other networks providing cells of coverage around one ormore base stations or nodes. Seed stations are simply stations that aremade available for use as intermediate relaying stations where necessaryand are typically placed at fixed positions (on lamp posts and on theroofs of buildings, for example) to assist in the opportunistic routingof messages between wireless stations. Seed stations are not fixedinfrastructure of the network and may even be removed when there aresufficient other stations in an area.

Seed stations in the ODMA network are, to all intents and purposes, justlike other wireless stations except that they are not used bysubscribers and generally remain stationary. However, there is no reasonpreventing seeds from being moving stations, located on trains orvehicles, for example. Although not essential, it is intended that most(if not all) seeds will either be provided with data defining theirabsolute position, or will have a means of determining their position tosome degree of accuracy. This would enable the surrounding stations toestablish their positions relative to a fixed absolute datum point(although this does not necessarily need to be a seed station).

In order to provide accurate positioning information, and depending ontheir location, the seeds may incorporate station based positioningsystems themselves (such as a GPS system, which may be useful if theyare intended to move) or they can be loaded with information from apositioning determining device (such as GPS) at the time ofinstallation. However, due to the constant re-evaluation of position inthe general ODMA network system, a fixed seed will gradually developposition information that should prove considerably more accurate thanmay be afforded through the standard station based GPS positioningsystem. This information could be provided to a central authority, whichcould authenticate the accuracy of the absolute position of the stationfor use by the other stations on the network. There may also be otherstations in the ODMA network that incorporate other station basedpositioning hardware. For example, GPS receivers might be provided incertain subscriber telephones and other devices. The above describedabsolute “position enabled” fixed seeds and any other independently“position enabled” stations, which can be referred to as “mobile seeds”,will help to provide the initial “accurate” absolute positioninginformation, as wireless stations are first added to the network.Although many wireless stations may initially be well out of range ofthe stations having absolute position information, it will becomeevident from this description that the network will grow and share thisinformation in a manner that will eventually (typically quickly)encompass almost all, if not all, the stations on the network.

In much the same manner as described with reference to the prevention ofdrift in the accuracy of the clocks above, it may be possible to haveone or more extremely accurate datum points for position referencepurposes, from which other stations can confirm their position withextreme accuracy. The determination and containment of cumulative errorfunctions with respect to the position will also operate in asubstantially similar manner, with each station utilizing the highestquality of position information with least error.

Each of the stations in the ODMA network will begin gathering neighborsthrough the slow probe process. In doing so they will each quicklyestablish whether there are any neighbors that have absolute positioninformation. This information may be provided in the probe together withthe station identifier. Some of these stations may be significantlyfurther away or have a poorer quality of connectivity relative to theother neighbors. However, there may be other stations among a station'sneighbors that are in a better position relative to these absolutepositions.

It should be clear that the closer one station is to another, the lessthe error that will be incorporated in calculating the distance throughthe techniques referred to above. The greater the distance of the hoptraveled by the signal, the greater will be the error function. If thereare many stations that are closely located with accurate positioninformation, then other stations will be able to establish theirpositions relative to these stations with great accuracy. Consequently,even if information about a station with a determined position that isfar away is passed through several short transmission hops or steps(each intermediate station directly or indirectly assessing its ownposition relative to the station identified as having a determinedposition, and from others that may be within its group of gatheredneighbors), as each hop is small there is minimal error passed on to thestation that is attempting to establish its location. This is becausemany small hops of good quality with excellent position informationprovide far more accuracy in determining position than one bad qualityhop with poor information. As each station gathers more neighbors withfixed absolute position information, each station can test the qualityof its information against information acquired through entirelydifferent sources; and gradually the positioning will becomeincreasingly accurate.

It should also be apparent that the neighbor stations will quickly beable to determine their relative positions to each other, even wheretheir positions may be uncertain geographically. When information isreceived that enables one of these stations to verify its actualposition, all the other stations will be able to establish their owngeographic positions almost immediately due to their prior determinationof relative position. In certain circumstances, relative positioning maybe all that is required. For example, two people wishing to meet up in alarge park may not need to know details such as latitude, longitude andelevation—they simply need to know how far to walk and the direction tobe taken in order to meet up. In other words, all they need is thevector comprised of distance and direction.

Alternatively, a station may only wish to know where certain otherstations are relative to each other, while not requiring absoluteposition, or even position relative to the original station as such. Forexample, a father may merely wish to be sure that his wife and child areconstantly close together, or a police dispatcher may requireconfirmation that police personnel are not separated from their firearmsor from their vehicles. Indeed in an emergency situation it may only beimportant to know the relative position of the station requiringassistance from the emergency personnel available.

In summary, positioning information may be required in respect of theabsolute position of one's own station; or the absolute position ofother stations; or the relative position of one's own station to anotherstation; or of another station's relative position to other stations. Ofcourse, absolute positioning knowledge enables relative positionknowledge automatically, while the reverse is not true. In any event,all of this position information may facilitate the provision of all thelocation based services and applications that are available.

In an ODMA network, it must be appreciated that many stations may bemobile and will be establishing their locations from other stations thatare themselves mobile. Intuition would suggest that a particular stationattempting to establish its location may well be several hops away froma wireless station with a fixed position (relative or absolute) or froman absolute position that is established independently of the network(stations with GPS or other positioning devices). However, in an ODMAnetwork the positioning mechanisms are also dynamic with “growingconnectivity”—where any stations initially having unknown locationultimately become “engulfed” by the position information gathered by thestations determining their own positions. The network station positioninformation “crystallizes” iteratively across the network. In addition,not all stations will be moving all of the time, so any stationattempting to establish its position will probably utilize informationreceived from stations that are known to be stationary as these will beconsidered more stable and reliable.

Some stations may need to be patient and wait for their neighbors toestablish their own positions; but it should be evident that asneighbors are gathered on an ongoing basis, the information necessary toestablish position will become increasingly available across thenetwork. This will mean more and more stations will have sufficientinformation to update their own position and pass on information toassist others. If necessary (and certainly at the initial stages) thestations can ramp up their probing signal strength to have a betterchance of identifying a neighbor further away that may have positioninformation, in order to obtain the necessary initial information, andthen power down again once an indication of position is established.

The iterative, crystallizing nature of the process is illustrated in avery simplified and merely indicative form in FIGS. 2 and 3. In FIG. 2(a) a geographic area of the network is represented, having a number ofusers. Some users are represented as being closely populated, others arespaced further apart. There are several fixed seeds in the area withposition information and some mobile seeds, or stations with positioningdevices, although it will be appreciated that the number of initialstations with position information, whether fixed or mobile, is lowrelative to the total number of stations.

The first step in the process is for the stations to gather neighborsand this is illustrated in FIG. 2( b). In the example illustrated, eachstation aims ideally to develop only 3 close neighbors, although it willbe evident that certain stations (some of which are indicated) haveestablished less than the minimum at this initial stage.

FIG. 3 shows the same network illustrated in FIG. 2 over time. At timet₀ (as shown in FIG. 3( a)), none of the wireless mobile stations in anarea have location information from the network. However, there areseveral fixed seeds interspersed throughout the area and there are alsosome mobile seeds, or mobile stations that have independent positioningsystems. At time t₁ (FIG. 3( b)) several stations have successfullydeveloped position information from the seeds and the stations withknown positions according to a first embodiment of the invention.Notably, stations in more densely populated areas determine some form ofposition (relative or absolute) more quickly. In FIG. 3( c) many of thestations that had only determined relative position before now haveneighbors with absolute position that enables these relative positionsto very quickly become absolute.

FIG. 3( d) shows time t₁ for position determination according to asecond embodiment of the invention. Here only absolute position isdetermined. As more and more stations are able to establish theirpositions, other neighboring stations will also be able to determinetheir own positions and the number of stations with known positions willgrow iteratively and exponentially as is shown at time t₂ (FIG. 3( e)).

In both of the illustrated crystallization mechanisms illustrated,ultimately, all of the stations on the network that are able to locateneighbors will be capable of establishing position to a greater orlesser degree of accuracy—then reassessing information and refiningposition as updated or alternative information is made available. Evenlonely neighbors, unable to develop the minimum number of neighbors, maybe provided with information from the other stations to establish theirposition (unless completely outside propagation range). However,depending on the distance, the quality of information may be relativelypoor and consequently less accurate.

FIG. 1 described a situation where three stations with known positioncould communicate their absolute positions to a station R and from thethree sources of position information the position of R could beestablished. However, if R could only hear the transmissions of thethree stations, but did not receive absolute position information, thenall that R could conclude is that the other stations are each a certaindistance from it. This principle is illustrated in FIG. 4( a), where astation A can receive the transmissions (or may have probed and receivedresponses) of three neighbors A1, A2 and A3, thereby determining thatthese stations are all within certain “orbits” of A at distances a1, a2and a3, respectively. However, station A would not be sure where on theorbits the stations are located. FIG. 4( b) indicates where the stationsare actually positioned relative to each other, but none of them candetermine this initially.

If all the stations illustrated could hear some or all of the probesfrom the other stations, or share information with each other, then moreconclusions can be drawn about their relative positions. This is theprimary concept of a first embodiment of the present invention, themechanism of which will now be described with reference to FIGS. 4( c)to 4(e). In the ODMA technology, each station gathers and maintainsneighbors; in the example of FIG. 4 station A has gathered threestations. In FIG. 4( c), it is apparent that A1 shares A3 as one of theneighbors that it has itself collected. In the example, A1 could havegathered other neighbors (in addition to A3) that may or may not includeA and/or A2, as each station in the network will be identifying andcollecting its best possible neighbors; and while A1, A2 and A3 may bebest for A, other stations may well be better for A1 (although here A3is shared).

In any event, in ODMA each neighbor will share information in respect ofits collection of neighbors maintained in its tables, so A1 will knowfrom A that A3 is one of A's neighbors, and A1 will also be able toestablish from A that the distance between A and A3 is a3. A1 will alsohave been told its distance a1 from A and A1 will consequently be ableto determine that the distance between A1 and A3 is a1 a3 bytriangulating. A3 will be receiving information from both A and A1 (asit is a close neighbor of both stations) so regardless of whether A orA1 are its own collected neighbors, it will know all three distances aswell. Consequently, all three stations know their relative distancesfrom one another, and although A3 could be at A3′ (an ambiguity), A1 andA can establish both distance and relative direction—in other wordsthere is a relative vector between them (these stations are shown inbold and now have relative position information). It should beappreciated that in this initial triangulation, the calculation is madebased upon highly accurate information that is shared.

FIG. 2( d) shows A2 has also gathered A3 as one of its neighbors. Asdescribed above, this means A2 and A can determine a vector between themdespite the ambiguity of A3's possible position at A3″. However, becausethe actual distance between A1 and A3 is known by A, it is clear nowthat A3 can only be in one place, so A3′ and A3″ are discarded. In otherwords, the shared information between the neighbors has enabled A toresolve the ambiguity and this can be communicated to all of A'sneighbors in the nest probe (which will pass the information on to theirneighbors). However, all that has been determined with great accuracy atthis stage is relative position (shown in bold), For station A thismeans that the cluster of stations still orbit around it as illustratedin FIG. 2( e), but at least it is in a fixed orientation or“constellation” at this point in time. In reality if the cluster choosesto appoint one station as a datum point (e.g. 0,0,0), then the stationscan all describe each other with relative bearings but they actuallyoperate in relative orientation in an undefined three dimensional space.

This is shown in FIG. 5. FIG. 5( a) illustrates that Station A and itsneighbors in FIG. 4 are in fact orientated in three dimensions relativeto each other. FIG. 5( a) shows that the cluster described in FIG. 4( e)is actually rotatable and moveable in any plane (the cluster isillustrated in various possible three dimensional orientations relativeto the absolute point at A). FIG. 5( c) shows that there may be a morecomplex three dimensional relationship with additional stations, but inthe figure point A and B are now know absolutely in the space. With twopositions fixed, the entire arrangement that had been only definedrelatively is now fixed to a greater degree, but is still rotatablearound an axis as indicated in FIGS. 5( c) and 5(d). If an additionalpoint C is fixed absolutely, in FIG. 5( e) then the positions of theentire three dimensional structure is fixed absolutely and every othernodal station can now be fixed absolutely. In the present invention,each station will have the information of each neighbors' station sothis information will be distributed through the network with minimaladditional probes.

It should be understood from FIG. 5( c) that the absolute positioninformation that is initially available to stabilize the overallposition determination in the network can be many hops away from thestation attempting to fix its absolute position. As this information isrelayed over high quality hops, and as the relative positions can beestablished with great accuracy, the accuracy of the positionscommunicated across the network is inherently precise. The abovedescription has illustrated an apparently static network forsimplification of the explanation. The invention must not be understoodas being limited in this respect as in reality, the inventioncontemplates a dynamic network of mobile stations.

It must be appreciated that, even in a highly mobile environment, thepositioning process can be very accurate if the probing mechanism isundertaken many times a second. Thus, if a first station requiresposition information relating to a second station that is movingrelative to the first station, the first station can transmit gradientgathering probe signals addressed to the second station at an increasedrate selected to provide enhanced resolution of the positioninformation. These gradient gathering probe signals can be transmitteddirectly to the second station, or via one or more intermediatestations.

For example, the fast (gradient gathering) probing in an ODMA networkcan take place several thousand times per second. In such circumstances,even if two vehicles were traveling towards one another at 180 km/h, inother words a cumulative speed of 360 km/h (or 360,000 m/h, or 100 m/s),if probing is taking place at 1,000 times per second, the vehicles willhave moved only 10 cm relative to each other between probes. In general,the increased rate of transmission of the gradient gathering probesignals is at least two times greater, and preferably at least an orderof magnitude greater, than a standard rate of transmission thereof. As aresult, even when stations are moving at relatively high speeds relativeto one another, the stations appear relatively “static” to one anotherwhen their positions are measured with enhanced accuracy.

The gradient gathering probe signals need only be transmitted at anincreased rate while the first station requires the enhanced positioninformation. Otherwise, the increased probing rate would consume networkresources unnecessarily.

FIGS. 6( a) to (f) relate to a more detailed description of the processof the second embodiment of the present invention. FIG. 6 is a series ofconnectivity diagrams showing five stations in an ODMA network, labeledA-E. As in the previous example, it should be appreciated that thestations forming the network may be devices of varying type. In thisillustrated example, there are telephone handsets (telephony), computersor PDAs (data provision, via the Internet, for example) and a seedstation. In the sequence illustrated, each of the stations has generatedup to four close neighbors, labeled 1-4 for each station. Some of theneighbors are shared as close neighbors between the stations (D3/E2 andC1/E1). In FIG. 4( a) all the stations lack position information(represented by circles), with the exception of the seed station E whichhas absolute position (represented by a diamond). In addition there aretwo close neighbor stations that have absolute position information fromthe outset, namely C1/E1 and D2 (both being represented by diamonds).Neither stations A nor B have any information from immediate closeneighbors regarding position.

(Under standard ODMA processes, however, B would have information aboutE from the probes sent by C. In this second embodiment the additionalinformation received through neighbors is of lesser relevance to thefixing of position.)

It will be immediately apparent that from the start stations C and Dwill be able to establish that they are within certain radii of the seedstation E, using the technique illustrated schematically in FIG. 1( a).In addition stations C and D will be able to establish that they areboth at either one of two particular points, as they each have absoluteposition information available from two close neighbors (refer to FIG.1( b)). Either of these two mechanisms for determining position mayalready provide sufficient accuracy for the purposes of stations C andD. Furthermore, surrounding neighbor stations may be able to assist inremoving any ambiguity in position, as discussed below.

FIG. 6( b) shows that the close neighbors of stations A to E inactuality each have several close neighbors of their own, some of whichmay already have absolute position information (represented bydiamonds). This determination of neighbors and position information forthese neighbor stations will have been acquired or determinedindependently from other stations in the greater network by similarprocesses as described here. These processes will be taking placesimultaneously across the network, outwardly from and inwardly towardsthe stations illustrated, but for simplicity only the mechanismsoperating in respect of the identified stations are described.

For purposes of explanation of the positioning process, the stationshave not been shown to be moving, although as indicated above they willbe capable of doing so in the ODMA network. Similarly, as in the firstembodiment, the neighbors being maintained adaptively remain static forillustrative purposes only, although the close neighbors could bechanging due to variations in the connectivity available. FIG. 6( c)shows the connectivity diagram after initial probing by the stations. Itcan be seen that close neighbors A1, C3, B2 and D3/E2 now have at leastthree of their own close neighbors that have fixed their absolutepositions (the fixed positions of these neighbor stations beingestablished by means independent of the example provided in respect ofstations A-E). This has enabled these stations to triangulate theirpositions from these neighboring stations. Consequently, stations C andD now have at least three neighbors with absolute position informationwithin one hop from which they can triangulate.

At a later time, as shown in FIG. 6( d), stations E3, C2, B1 and A4 havealso successfully obtained absolute position information throughtriangulation, thereby providing station D with 3 close neighbors andstation C with four close neighbors from which to determine position. Asthe four stations around station C have not gathered their positioninformation from the same neighbors, station C will have additionalinformation that will allow triangulation from different stations andthereby facilitate testing of the accuracy of the position established.From this information, other stations, even position-enabled stations,such as the seed station E, will themselves be able to test and refinetheir own positions using position information obtained from the otherstations, enabling the overall level of positioning information in thenetwork to improve in accuracy through the different informationopportunities made available.

Although it might appear redundant for position-enabled stations toparticipate in such a process of refining their position information, itwill be understood that GPS and other positioning systems are onlyaccurate to a certain degree (say, to within 10 to 15 meters) unlessenhanced with additional data or equipment. As the other stations areable to consolidate and refine their positions from alternate sources ofposition information, it may become apparent that the position of a seedstation is not actually all that accurate. If there are many otherstations near the seed station, the accuracy attainable couldtheoretically be of the order of centimeters as even radio propagationwill provide very accurate distance measurements over short transmissionhops of high quality. It is also possible that a seed station may havebeen set up inaccurately (for example, the seed station may have beeninadvertently moved after being programmed with GPS-derived positioninformation, or it could be faulty). The more stations made available,the more accurate all the positioning will be in the network as a whole,especially in respect of each station relative to the others. If certainstations have a higher quality of position information, the station willbe preferred to others in the testing process. In this way, anyanomalies should be easily highlighted and can be corrected.

By the time shown in FIG. 6( e), station B now has sufficientinformation with which to triangulate and by the time reflected in FIG.6( f), station A is able to determine its absolute position.

It is important to reiterate that regardless of the embodiment used,prior to each station receiving information regarding position (relativeor absolute), the station may have location information that issufficiently accurate for the purpose required. The main feature torecognize is that the positioning becomes increasingly accurate as moreinformation is made available through neighbor gathering. Consequently,the connectivity and positioning information expands and grows veryquickly to cover the entire network. Even though, station A in FIG. 6for example may have been located in a seemingly inaccessible location,such as an underground basement, with neighbor gathering through slowprobing, the location of station A may still be determined. Aspreviously indicated, even though station A may not have initially knownits absolute position it may still have sufficient information toestablish its relative position to station B and the other stations.

This is a significant advantage of the process, enabling stations whichwould otherwise have no means of establishing position, such as stationslocated indoors or underground, to be located through the neighborgathering process. Through the probing process and the multiple hopsavailable to stations with the information required, there areeffectively many stations that can find hard to reach stations. The morestations provided, the more difficult it will be for a station to remainundetected. Another advantage is that, as some stations have accurateinformation being provided on an ongoing basis, any stations that havepoor information with which to calculate position initially will be ableto analyze information received and refine the earlier iterations in thecalculation of position. This activity is similar to the ODMAopportunity driven routing mechanism for communications, in that themore neighbors available, the greater the number of optimalopportunities available as choices for a station to locate high qualityinformation on position and relative movement from its neighbors.

The ODMA communication network is able to establish station positioninginformation in real-time, and the more stations in the network thegreater the accuracy will be. While the movement of many of the stationsmay complicate the process on the one hand, as positions are constantlychanging, the relative movement does provide additional informationwhich, perhaps a little counter-intuitively, further enhances accuracyand the amount of information available.

As previously indicated, some stations will be able to relay the factthat they are not moving, and may even provide a predetermined gradingof the quality of the positions determined. The longer the stationremains immobile the more accurate the position will likely become.Being cognizant of the reliability of certain information, stations thatare mobile will utilize these stations with enhanced accuracypreferentially in comparison with their other neighbors. However,stations will also be able to detect relative movement of their ownposition or that of other stations. As a station moves, a stations willrecognize that the distance is changing and in combination with otherstations will be able to calculate speed and direction by geometrictechniques.

However, there are also dynamic signal characteristic effects generatedthat may be monitored and these characteristics provide information whenanalyzed, namely changing signal strength, phase shift, Doppler shiftand multi-path distortion. Should two or more stations receiveinformation through probing in relation to the same moving station, thencollaboratively these radio characteristics will provide information inrespect of the direction traveled and the speed of travel. For example,if all neighbors detect the Doppler shift, motion will be detected andbetween them, the stations will have sufficient information to makesense of the movement in terms of direction and speed in real time.

When analyzing signal characteristics, there are a number of issues thatimpact on the transmission quality of signals between stations and thisinformation can be analyzed to provide positioning and relative movementof stations. As radio frequency signals take different paths from asource to a destination station, part of the signal may travel to thedestination station directly, while another part may be reflected ordeflected off or through obstructions prior to reaching the destination.As a result of the reflection or deflection, part of the signal willexperience a time delay as it takes a longer path and will lose moreenergy than the part of the signal following a direct route. Multi-pathdistortion is a form of interference that occurs as a consequence of thedifferent paths taken by the direct and deflected signals, as theysubsequently combine, causing distortion to the desired waveform.

As a general rule, the signal strength will be affected primarily as aresult of the distance traveled (usually due to free space loss as thesignal power is spread out over the surface area of an increasingsphere). However, signal strength will also diminish through lossesencountered by passing through certain media and also by virtue of themulti-path propagation problems (multiple copies of a signal may arriveout of phase, adding destructively and lowering the signal levelrelative to noise). Consequently, if the path is line of sight thensignal loss may not be severe, but in urban surroundings the path of thesignal is likely to reach the destination station after reflection,diffraction, refraction and scattering of the signal. A fast relativemovement between stations will result in the receiving stationsexperiencing rapid fluctuations of the signal strength (in amplitude andphase).

While analysis of the signal characteristics can lead to betterassumptions, it is still possible to interpret the informationincorrectly. For example, the strongest signal will generally beinterpreted to be the direct signal, with the weaker signals interpretedas deflected signals. However, if the main signal traveled through ahighly attenuated path (through walls or thick vegetation) it may bethat the deflected signals are stronger and it will be difficult todifferentiate the direct signal from the multi-path signals—and thiswill mean more errors in any distance calculations. With more stationsavailable for assessment calculations these peculiarities can berecognized very quickly as the stations are obtaining their owninformation from different positions relative to the station and itsneighbors.

In addition, because some of the stations move, the inconsistencies willbe picked up more easily by virtue of the new calculations processed. Asdirect and deflected signals are better differentiated, stations will beable to determine whether they themselves have been moved, or whetherone or more of their neighbors have moved, as well as the direction andspeed of the movement. The information could be utilized as a factor indetermining whether to prefer information received from one station overthat received form another.

In a cluttered environment there is less likelihood that the source anddestination stations will be in direct line of sight—but there is astrong chance that many of the relaying stations are indeed in line ofsight from each other. This means high quality information is beingpassed on along the route.

It will be appreciated that if any stations use a directional antenna inthe network then only two other neighbor positions would be required tofix geographical position, and if there is additional information fromanother party the station can quickly determine whether there arereflected or refracted signals or multi-path distortions as well. Inaddition, the mobility of the stations increases the chance of thesediscrepancies being noticed and corrected, enabling more advancedtechniques to be used that can demodulate or separate the waveformsusing encoding in the waveforms et cetera.

FIG. 7 is illustrative of some of the processes taking place around asubset of the stations shown in FIG. 2. In FIG. 7, three stations A, Band C are shown, each of which has developed ten neighbors by probing.The extent of propagation transmission strength of probe signalsrequired from each station is shown, such that each station has gatheredten stations as neighbors, of which five are “close neighbors” andlabeled 1 to 5. Station A requires the least power to gather the minimumnumbers of neighbors as they are in a closely populated area. Station Brequires the greatest power.

Of the stations shown, it can be seen that only station C has threeneighbors having known position within its group of detected neighbors,so station C can establish its position by triangulation immediatelyusing the mechanisms of the second embodiment of the invention describedabove. It can also be seen that certain neighbors of the stations areshared with other stations. For example, neighbors C5 and A2 are amongststation B's detected neighbor stations.

FIG. 8( a) shows the stations of FIG. 7 that have three stations ofknown position within their ten detecting neighbors and within themaximum power levels needed to gather ten neighbors with establishedfixed positions. Stations D, E, and F are accordingly able totriangulate and establish their own positions.

FIG. 8( b) shows the stations of FIG. 8 a) a moment later, afterstations E, H, and I have been able to triangulate their positionsfollowing the position fixing of stations C, D, E, and F. It will beappreciated that all these stations now have more than three stationswith absolute position from which to triangulate, enabling testing andrefinement of the positions already determined.

FIGS. 8( a) and 8(b) show the mechanism where some of the stations arespaced relatively far apart from one another. FIG. 9 illustrates some ofthe mechanisms that may take place when stations are in more denselypopulated areas. In FIG. 9( a) for example, the transmission powerbounds of station A (of FIG. 7) and two of its close neighbors (A3 andA4) are shown. It can be seen that because the stations are closetogether, each of the stations is able to obtain the minimum number ofneighbors at relatively low power settings. However, this means that allof the stations with fixed absolute position information are notmaintained as neighbors, leaving stations A, A3 and A4 only able todetermine relative position information.

However, the slow probe process provides essential information about theneighbors of a station's neighbors. For example, in FIG. 9( b), stationA will maintain station A4 as a neighbor and in so doing will belistening to the probes received by station A4. Station A willconsequently know that station A4 has two neighbors that have absolutefixed positions. Station A4 itself will be attempting to determine itsposition and will be able to establish that it is at one of twopositions (refer to FIG. 1( b)). Station A4 will know the distance toeach of its neighbors and many of the neighbors of these neighbors willknow the distance to station A4. Between them, as some stations will notbe able to hear station A4 despite it potentially being close, thestations will quickly be able to resolve the ambiguity and determine thetrue position of station A4 from the two available alternatives. Once afixed position for station A4 is established, station A will have twostations from which to establish its position using the methodsdescribed in the second embodiment. The other station A neighbors may beable to assist in resolving any ambiguity in station A's true positionfrom the two available possible positions, or station A3's positioncould soon be determined, as represented in FIG. 9( c).

Once the absolute position of station A3 is fixed, station A cantriangulate its own position as shown in FIG. 9( d). It should beappreciated that all of the stations surrounding station A will havebeen able to each determine their relative positions in relation totheir neighbors. Consequently, as soon as the position of one of thestations becomes fixed absolutely, all the others will be able todetermine their own absolute positions almost immediately. It shouldalso be apparent that even without the knowledge of station A3'sposition, station A could have resolved the ambiguity surrounding itsposition. The fixing of station A3's position enables station A toverify the position previously established and improve the accuracy.This scavenging of information to resolve ambiguity and improve accuracyis a key benefit of the ODMA positioning process through probing,enabling conclusions to be made through the stations each mutuallyassisting each other.

If there were only a few neighbors in a sparsely populated network,errors in any absolute position provided would be passed on from stationto station. However, the relative positions of the stations to eachother would be very accurate, as the determination of distance can bevery accurate depending on factors such as the distances involved, themechanisms used and the quality of the connectivity between stations. Asmore stations become available on the network, that have establishedtheir own location accurately, the better the quality of informationthat is accessible for analysis and the more accurately the station'sown position can be determined.

For example, in the event that the triangulated positions that arecalculated at a station conflict (using information from different setsof stations), with further analysis it may be possible to determinewhere the inaccuracy arises. If there is convergence on the positionfrom several sites on a simultaneous basis then there is a stronginference that one position determination is reliable, and in thismanner the network positions can be corrected on an ongoing basis andbecoming increasingly accurate. Moreover, the stations will be able toassist each other in resolving ambiguities as will be made evidentbelow.

This process is further illustrated in FIG. 10 using mechanismsdescribed in the first embodiment of the invention. In FIG. 10( a) forexample, as in FIG. 4 above, station A readily establishes distances toits neighbors (three of which are illustrated (A1, A2 and A3)). A1 hasneighbors A11, A12 and A13, as shown in FIG. 10( b). As A1 shares A2(also A11) as a neighbor, the relative positions of A, A1 and A2 arequickly determined. Similarly, A13 has A2 (also A131) as a neighbor, sothe relative position of A13 can be established. However, because astation receives all the information of the neighbors of its ownneighbors, this can be shared two hops ahead. So in the illustratedinstance, A1 and A2 will know the distances from themselves to A andfrom themselves to A13. A will consequently know its neighbors'neighbors, and consequently knows the distances between A1 and A13 andbetween A2 and A13. From this, A will know exactly where A13 is relativeto A (and vice versa) despite the fact that the stations are two hopsaway and not in communication with each other. Indeed the neighbortables held by the stations could maintain information of another levelof neighbors (the neighbors of A13 through A1 and A2, for example), thatwould enable position to be determined over three hops. If this were thecase, A would realize that A133 is a station with absolute positioninformation, as well as C1 and C4.

In any event, as the stations determine their relative positions, byFIG. 10( d) a station with absolute position information is a neighborof A13 and A2. If other stations in the network, even if far apart, haveabsolute position, they can establish absolute position in subsequentcommunications from the stations with this information. It must again beborne in mind, however, that the mechanism described above is happeningin all directions outwardly from each and every station, so station Awill be receiving relative information (to two hops) initially fromseveral sources, and then absolute information from several sources(FIG. 10( e)). So A and the other stations will ultimately be in aposition to fix their absolute positions, then verify or refine thesecontinuously. The crystallization effect will be relatively rapid, thenvery rapid when absolute positions are available, and then consistentlyreadjusted.

FIG. 11 shows an alternative means for station A to gather the minimumnumber of fixed stations—it can simply increase the propagation strengthof its probe signals until it reaches sufficient stations. However, itis preferable that the ODMA network as a whole operates at lower powerlevels as this increases the overall efficiency, by minimizinginterference and collisions of transmissions, for example. Thus,although this method certainly may provide the required informationquickly, the accuracy will be reduced by virtue of the greater distancesinvolved and the chaotic signaling that will be created. Of course thisprocess will be refined as more positions in the network areestablished.

However, before this alternative process is initiated, it is much morepreferable that stations slowly generate neighbors and remain patient.If necessary, messages could be transmitted through the network toindicate that good connectivity is available, as this will communicateto each station that the station is not completely isolated and will belocated in due course. Alternatively, the isolated station could senddiscrete enquiries to its neighbors, or to certain designated stations,or with an instruction to locate certain categories of station andredirect the message to the station so that it can reply withinformation relating to the progress that may be made in locating theisolated station. This will help to mitigate the need for increasingtransmission power levels and should reduce the chaotic consequences ofdoing so.

Provided there is connectively from source to destination, thengradually all network station positions will be determined, even ifthere is only one datum point. In a communications network, messagingconnectivity could be established through the processes described in WO2005/062528 entitled Probing Method for a Multi-Station Network andPCT/IB2006/001274 entitled Multi-Medium Wide Area Communication Network.If the other station can be communicated with in this manner, then it isclear that there is connectivity to that station and the positioningprocess can be undertaken. If necessary, the position of either thefirst, requesting station or the position sending station can be set asa datum point (for example, in an x, y, z dimensional space the datumpoint could be set as (0,0,0)).

If a first station wants to know the position of another station in thenetwork, it could send out a position request message as a regularcommunication message, which in turn could initiate a positioningprocess if appropriate. The position request message could be addressedto a central authority maintaining position data and/or positiondetermining data of stations in the network, or could be sent to anyother appropriate station that may have this information, or access tothe information, including neighbors of the first, requesting stationfor onward transmission to the other station. Alternatively the first,requesting station could address the position request message directlyto the other station, and the latter station could transmit a messageback to the first station via the network with the required positioninformation, or initiate a position gradient back to the requestingstation.

If the requesting station provides the datum (broadcasting to everyonewhere it is), then other neighboring stations will determine theirpositions relative to the requesting station, with the certainty ofposition information expanding like a crystalline structure, until thedesired station is located. Relative position or absolute position, asthe case may be, could then be communicated as available, but in eitherevent, there will be a relative vector available in respect of thestations.

Alternatively, the sending station can generate the crystallizationprocess from itself as the datum point. This would grow outwardly untilan absolute datum is reached and communicated back to the station.

Indeed, any station could initiate a fast probing mechanism to determineposition even in circumstances where the other stations are notmaintaining position continuously. In such circumstances, the stationattempting to determine its position will transmit probes with certaininstructions, for example asking other stations to initiate probingthemselves. The extent of the probing could be specified to apply tostations receiving the probe within a predefined number of transmissionhops from the station wanting to determine its position; and the extentof the probing from the recipient stations could also be limited to acertain number of hops form each of these stations. From thisinformation stations would quickly establish at least relative positionswith respect to one another, and if the requisite number of stationswith absolute position information were located within the specifiednumber of hops, the “crystal” expanding from the original station willbe fixed absolutely; enabling all stations involved to establishposition. If absolute position stations are not found, or if a desireddestination is not located within the crystal generated, the initiatingprobes could now specify an increased number of predefined hops to beprobed in order to expand the crystal growth in an attempt to locate thedesired stations (either specific destinations or stations with positioninformation). In this manner, position determination might only beactivated “on demand” by stations in the network when required or for solong as needed, and in the process the stations involved would assesstheir own position which could be recorded. If a desired destinationstation is located, the gradient between the originating and locatedstations could be maintained for as long as is desirable for thepurpose, and then stopped to minimize usage of network resources. Ofcourse, in a network not requiring ongoing position information, thenetwork itself (or portions thereof) could be asked to undertake thisprocess intermittently from one or more stations to establish stationpositions and then to stop.

The slow probing process has the primary role of gathering neighbors ofhigh quality. In this mechanism, the positioning crystallization processis first generated and then requests are made for position information.However, it is possible to utilize the fast probing process to findother stations, developing the crystallization through the networkbetween the stations until it finds the desired station. A “distancegradient” could then be built back to provide the relative vectorbetween source and destination stations and maintained “on demand”.

In FIG. 12( a), a station X is attempting to establish the whereaboutsof a station A1. Although A1 is three or more hops away, X can send outa fast (or gradient gathering) probe signal looking for A1. Oncelocated, A1 will respond and a gradient will be returned through thestations, each providing the distances and directions available betweenthe intermediate stations, from which X can establish a relative orabsolute vector to A1, as the case may be. FIG. 12( b) shows that thegradient could be defined through various combinations ofintermediaries. It may be that a route through a greater number of highquality hops (e.g. shorter hops through a1-a5) is more accurate than asmaller number of hops (longer, or poorer quality hops 1-3); and thebetter choice from which to determine position might be assessed usingcumulative errors.

The fast probing of this nature could be maintained simply to locate astation for a particular purpose and then the probing will stop, or itcould be maintained for a specific period (tracking a car at speed, ormovement between stations in an emergency situation, for example).

If the position of a station is determined, certain services orapplications could be provided in the region or in a targeted fashion.For example, advertising, notices or information could be provided inthe area of the station or in certain areas defined according to thelocation. So in such circumstances advertising banners could be utilizedor users in the neighborhood (all users, or selected categories ofusers, or only certain selected users) could be provided withinformation or video streams to assist in finding a missing child; orstations and billboards that are in locations or en route to where anescaped criminal was or will likely be in the future could be fedinformation based on the movements of the criminal in order to obtaininformation, evidence or assistance. Specific police or other personnelat known locations can be given very specific information on a relativeor absolute position basis.

An important feature that arises from the described ODMA positioningprocesses is a “neighborhood watch” mechanism that is enabled by virtueof the slow probing process. Each “neighborhood” or group of neighborsgenerated by the stations accumulates and retains a substantialcollective and distributed knowledge. This knowledge can be accessed andassessed if necessary to establish positions, which is especiallyrelevant in otherwise problematic circumstances.

Stations in the network of the invention maintain certain signal relatedinformation in the course of the standard communication process andalgorithms and also additionally maintain a record of the last knownposition of neighboring stations. If a station is switched off ordestroyed, or even if the battery merely fails, the other stations willhave access to information in their memory in relation to the last knownposition and the time since the position was determined.

Even if a position had not been determined, the information on thesignal strengths of the various neighbors can be reevaluated from theneighbor tables in order to determine the position and direction thathad been traveled to enable certain conclusions to be drawn from thehistory retained. In addition the stations maintaining the informationwill also know the other stations that were detecting or close neighborsof the missing station. This suggests the stations that may be enquiredfrom regarding position determination and provides the capability forcertain assumptions to be made; for example two stations may have beenrecorded as traveling side by side for a relatively long period and itis consequently likely that the stations are still close together. Twopeople may have been traveling in a vehicle together when one stationhas run out of batteries. This is also similar to a parent asking peoplein the immediate vicinity if they have seen their lost child; or askinga known friend if the child is with them; or asking someone's last knowntraveling companion where they were last seen and in what direction theywere traveling.

In an emergency situation the neighborhood will still have an up to dateknowledge of the last known position and the closest geographicallypositioned neighbors. This will obviously provide emergency personnelwith an accurate place to start looking for the station requiringassistance. Furthermore, as the knowledge is distributed to many otherstations it is difficult to avoid the station user from being located.Even if a kidnapper, for example, switched off or destroyed a victim'sstation there will be many neighbors who can pinpoint the station'sposition immediately prior to this and it may thus even be possible todetermine who approached the victim in the first place. This capabilityobviously has a myriad of applications, including the assessment of caraccidents, hit and run incidents, et cetera. To further facilitate thisprocess, updated position information could be sent periodically bystations to Authentication Servers that can be queried if necessary fornearest neighbors (and even for information regarding stations withabsolute position).

Furthermore, a reduced capability to communicate could be obviated tosome extent through the subsequent steps taken by the failing unit andby the immediate neighbors. For example, if a station's antenna isdamaged or if the battery level is very low, the signal propagated bythe station could be sent only to very closest neighbors on anoccasional basis in order to remain in limited contact and reduce powerconsumption. If a station was hidden from the network, the dynamicnature of the mobile stations should increase the chance of a closeneighbor being developed through the slow probing process or momentarilythrough the limited propagation basis in order to locate the stationopportunistically, especially if other stations on the network werealerted to the fact that a station was missing and was in need oflocation in emergency circumstances.

In a standard wireless networking environment these benefits are notreadily achievable, especially at the level of accuracy provided by theODMA network system. A base station would simply have to retain too muchinformation from so many stations to provide a workable solution withoutcongestion and delay. In the ODMA environment the information isdistributed only to immediate neighbors and is continuously updated. Inthe event that the information is needed, the stations can readilyestablish gradients to the necessary stations through fast probingtechniques. This process is extremely quick, even in large networks.

Another application that arises by virtue of the “neighborhood watch”capability is that unusual or unwanted activities may be monitored bythe network and if necessary other stations can be alerted. For example,if a station is moving at an unexpectedly high speed, or if a station islocated in a certain prohibited area or in close proximity with anotherprohibited or undesirable specified station, certain appropriateresponses can be made. These responses could include distributingknowledge quickly to neighbors or even specific emergency stations, orto a central authority.

This monitoring capability in real time will highlight unlikely,undesirable, or exceptional cases. The potential applications andresponses are limitless and could include vehicle tracking, inventorymanagement applications, monitoring of children, monitoring of peopleunder probation or court injunction, or merely alerting networksubscribers to the fact that they are near certain facilities such asfuel stations, police stations or restaurants, for example. Moreover incatastrophic situations, immediate responses could be takenautomatically—an aircraft in distress might transmit at high power itsposition and also download details from its “black box” data recorder incase this is destroyed should it crash. The knowledge would be dumped toany randomly available stations in order to download all the informationbefore the unit was destroyed. Mid-air collisions between aircraft couldalso be avoided by alerting each aircraft of the danger, et cetera.

In addition, it should be appreciated that in the context of manypotential applications the level of complexity of the station unitsincorporated in the network may be very low. For example, in monitoringthe relative movement between certain stations as described above, suchas the distance between a mother and child, or the position of a policeofficer relative to his/her firearm and/or other officers, thefunctionality of these devices could be relatively unsophisticated.These units could possibly utilize the mainstream ODMA communicationsystems for positioning purposes, but not necessarily. If necessary,these simplified stations could merely probe and gather neighbors fortheir positioning information (whether through propagationcharacteristics or timing probes or by other means) and establishdistances and other relevant data. Conventional ODMA stations couldperhaps recognize the simplified stations as helpful neighbors forpositioning applications, but could also disregard them as potentialrelay stations for message transmission in the operation of a standardODMA communication network.

In principle, a network could be formed only for positioning andtracking purposes without the need for an ODMA communication network assuch, although the basic ODMA neighbor gathering techniques as describedwould be carried out. In this manner, the exemplified vehicle tracking,inventory management or prisoner tracking solutions could either operateas stand alone networks, or could also be tied to other conventionalnetwork systems or other mobile network products, with or without usingthe ODMA communication network.

This form of positioning network would address many of the VOIPpositioning problems experienced by non-ODMA communication networkunits. While it would be preferable to have the ODMA relay communicationprocess to transmit the determined position data to some central controlstation, or to stations requesting the whereabouts of a particularstation, in principle this could be reported through some othercommunication means.

1-46. (canceled)
 47. A method of operating a network comprising a plurality of stations each able to transmit and receive data so that the network can transmit data between stations via at least one selected intermediate station, the method comprising: monitoring, at each station, the activity of other stations on the network to establish the availability of neighbor stations having connectivity with the monitoring station; transmitting probe signals from each station, other stations which receive the probe signals from a probing station responding directly, or indirectly via another station, to the probing station to thereby indicate their availability as neighbor stations able to receive or relay data; transmitting position data and/or position determining data in at least some of the probe signals and/or in responses to probe signals, the position data including data indicative of the absolute or relative position of a station transmitting a probe signal or a response signal, and the position determining data including data usable by a station receiving a probe signal or a response signal to determine the absolute or relative position of the station and/or other stations; maintaining, at stations which receive probe signals from one or more probing stations and/or response signals from one or more responding stations, position data and/or position determining data received from selected ones of the probing and/or responding stations; and at one or more of said stations maintaining said position data and/or position determining data, utilizing the position data and/or position determining data to determine the absolute or relative position of said each station and/or other stations, thereby enabling any station to determine its own position or the position of another station in the network either as an absolute position or relative to other stations.
 48. A method according to claim 47 wherein the position data and/or position determining data in the probe signals includes data indicating the absolute position or relative position of nearby stations selected by the station transmitting the probe signals.
 49. A method according to claim 47 wherein the position data and/or position determining data is used to determine the relative or absolute position of other stations in direct communication with said each station, and also other stations not in direct communication with said each station.
 50. A method according to claim 47 which is operated in a communication network in which the stations can transmit a message from an originating station to a destination station via at least one opportunistically selected intermediate station.
 51. A method according to claim 47 which is operated in a network provided primarily for purposes of tracking or locating stations in the network.
 52. A method according to claim 47 including selecting, at each station, a channel for the transmission of probe signals to other stations, other stations which receive the probe signals from a probing station responding directly, or indirectly via other stations, on the selected channel.
 53. A method according to claim 47 including transmitting clock data in the probe signals, and utilizing the clock data to determine the time taken for the probe signals to propagate between stations and hence the distance between said stations.
 54. A method according to claim 53 including synchronizing clocks at the stations of the network, with updated timing data for this purpose being transmitted from a central timing authority to the other stations.
 55. A method according to claim 54 wherein the acceptance or rejection of said updated timing data at any station is determined in response to a cumulative error function calculated in respect of the transmission of such data, relative to other prior or simultaneous transmissions of such data received at said station, thereby maintaining a high level of accuracy in respect of the synchronization of clocks at each station of the network.
 56. A method according to claim 47 wherein the position data comprises position information indicating the position of one or more stations to a predetermined degree of accuracy.
 57. A method according to claim 56 wherein the position data comprises absolute position information obtained from a station equipped with a station based positioning system, or a station with a known fixed location.
 58. A method according to claim 47 wherein the position data comprises relative position information indicating the position of one or more stations relative to other stations.
 59. A method according to claim 58 wherein the relative position information is obtained by stations determining the approximate distance between themselves utilizing transmission power and/or path loss data in probe signals transmitted between such stations.
 60. A method according to claim 58 wherein the relative position information is obtained by stations determining the distance between themselves utilizing timing data extracted from probe signals transmitted between the stations.
 61. A method according to claim 60 wherein the timing data includes processing delay data inserted into reply probe signals by stations responding to received probe signals, the processing delay data indicating the time taken at a station responding to a received probe signal to process the received probe signal.
 62. A method according to claim 58 including obtaining position information indicating the position of one or more stations by triangulation.
 63. A method according to claim 57 comprising utilizing a combination of absolute and relative position information to determine the absolute position of further stations by determining their position relative to other stations that have previously determined their own absolute positions, so that such further stations that are unable to communicate directly with other stations that have absolute position information can nevertheless determine their own absolute position indirectly.
 64. A method according to claim 57 including providing a number of seed stations, each of which is able to determine, or is provided with absolute position data defining, its own absolute position with relatively high accuracy, other stations transmitting probe signals to and receiving probe signals from the seed stations thus obtaining absolute position information from the seed stations to determine their own absolute positions, and further stations transmitting probe signals to and receiving probe signals from said other stations thus obtaining absolute position information from said other stations to determine their own absolute positions.
 65. A method according to claim 54 wherein each station selects received probe signals from which to extract position or timing data according to the extent to which such received probe signals are determined to contain position or timing data of a high quality in terms of distance measurement capability or clock synchronization.
 66. A method according to claim 65 comprising analyzing received probe signals to determine whether or not they are transmitted during optimum peaks of opportunity.
 67. A method according to claim 65 comprising measuring path loss and/or multi-path distortion in such received probe signals, and selecting probe signals having low path loss and/or low multi-path distortion for extraction of position or timing data therefrom.
 68. A method according to claim 47 wherein stations include data in their probe signals relating to the length of time they have remained static, other stations receiving the probe signals utilizing position data and/or position determining data preferentially from stations that have remained static for the longest periods.
 69. A method according to claim 47 wherein stations include auxiliary data in their probe signals relating to one or more of the following the number and/or quality of transmission hops between stations identified in the probe signals; age data indicating the age of timing data or position data and/or position determining data included in the probe signals; the stated or determined level of accuracy of position information relating to one or more stations identified in the probe signals; and quality data indicating whether the probe signals have been sent at peaks of opportunity, other stations receiving the probe signals utilizing position data and/or position determining data therein selectively depending on the nature of the auxiliary data included in the received probe signals.
 70. A method according to claim 47 wherein the probe signals are transmitted on probe channels defined by a central authority, thereby reducing interference and preventing jamming or interception of the signals.
 71. A method according to claim 47 wherein stations maintain historical position data of other stations for a predetermined time after such other stations have lost connectivity with one another, the historical position data being retrievable to determine the last known position of a station with which connectivity has been lost.
 72. A method according to claim 47 wherein stations utilise variations in data in probe signals or other characteristics of the probe signals, arising out of relative movement between stations, to resolve ambiguities in relative position data and/or position determining data in the probe signals.
 73. A method according to claim 47 wherein the nature or quality of a service available from a station in the network is adjusted according to the determined absolute or relative position of said station and/or other nearby stations.
 74. A method according to claim 73 including providing information to a user of a station relating to facilities, objects or persons, or other stations near to the determined position of said station.
 75. A method according to claim 47 wherein position information relating to a station is determined by transmitting gradient gathering probe signals between stations, directly or via one or more intermediate stations.
 76. A method according to claim 75 wherein the gradient gathering probe signals are transmitted at an increased rate selected to provide enhanced resolution of the position information.
 77. A method according to claim 76 wherein the gradient gathering probe signals are transmitted at an increased rate only while the position information is required.
 78. A method according to claim 47 wherein a first station requiring position Information relating to another station in the network transmits a position request message addressed to a central authority maintaining position data and/or position determining data of stations in the network; to one or more neighbors of the first, requesting station for onward transmission to the other station; or directly to the other station.
 79. A method according to claim 78 wherein the station whose position is required transmits a reply message to the first station via the network with the required position information.
 80. A method according to claim 78 wherein the first station transmits a gradient gathering probe signal addressed to the other station via one or more intermediate stations, said other station transmitting a response via one or more intermediate stations to thereby create a gradient through the intermediate stations, the gradient providing information enabling a relative or absolute direction vector to be established between the first station and said other station.
 81. A network comprising a plurality of stations each able to transmit and receive data so that the network can transmit data between stations via at least one selected intermediate station, wherein each station in the network comprises a transmitter, a receiver and data processing means and is operable to: monitor the activity of other stations on the network to establish the availability of neighbor stations having connectivity with the monitoring station; transmit probe signals to other stations and receive probe signals from other stations, so that other stations which receive the probe signals from a probing station can respond directly, or indirectly via another station, to the probing station to thereby indicate their availability as neighbor stations able to receive or relay data; transmit position data and/or position determining data in at least some of the probe signals and/or in responses to probe signals, the position data including data indicative of the absolute or relative position of a station transmitting a probe signal or a response signal, and the position determining data including data usable by a station receiving a probe signal or a response signal to determine the absolute or relative position of the station and/or other stations; maintain, at stations which receive probe signals from one or more probing stations and/or response signals from one or more responding stations, position data and/or position determining data received from selected ones of the probing stations and/or responding stations; and utilize the maintained position data and/or position determining data to determine the absolute or relative position of said station and/or other stations, thereby enabling any station to determine its own position or the position of another station in the network either as an absolute position or relative to other stations.
 82. A network according to claim 81 wherein each station is operable to determine the absolute or relative position of other stations in direct communication with said station, and also other stations not in direct communication with said station.
 83. A network according to claim 81 wherein each station includes a clock and is arranged to transmit clock data in the probe signals, and to utilize the clock data to determine the time taken for the probe signals to propagate between stations and hence the distance between said stations.
 84. A network according to claim 83 including a central timing authority for transmitting updated timing data to the stations of the network, and wherein each station is arranged to synchronize its clock with the clocks of other stations of the network utilizing the updated timing data.
 85. A network according to claim 84 wherein each station is arranged to accept or reject said updated timing data according to a cumulative error function calculated in respect of the transmission of such data, relative to other prior or simultaneous transmissions of such data received at said station, thereby maintaining a high level of accuracy in respect of the synchronization of clocks at each station of the network.
 86. A network according to claim 81 wherein at least some stations comprise a station based positioning system or are programmed with position data corresponding to a known fixed location.
 87. A network according to claim 81 wherein each station is adapted to determine the approximate distance between itself and other stations utilizing transmission power and/or path loss data in probe signals transmitted between the stations.
 88. A network according to claim 87 wherein each station is adapted to obtain position information indicating the position of one or more other stations by triangulation.
 89. A network according to claim 81 including a number of seed stations each able to determine its own absolute position with relatively high accuracy, so that other stations transmitting probe signals to and receiving probe signals from the seed stations can obtain absolute position information from the seed stations to determine their own absolute positions, and further stations transmitting probe signals to and receiving probe signals from said other stations can obtain absolute position information from said other stations to determine their own absolute positions.
 90. A network according to claim 81 wherein the data processing means of each station is operable to analyze received probe signals to determine whether or not they are transmitted during optimum peaks of opportunity.
 91. A network according to claim 90 wherein the data processing means is operable to analyze received probe signals by measuring path loss and/or multi-path distortion in received probe signals, and to select probe signals having low path loss and/or low multi-path distortion for extraction of position or timing data therefrom.
 92. A network according to claim 81 including a central authority to define probe channels for the transmission of the probe signals, to reduce interference and prevent jamming or interception of the signals. 